In field-oriented regulation, a direct-axis voltage (Ud) and a quadrature-axis voltage (Uq) are determined as manipulated variables of the regulation system from the measured actual regulating value, such as the phase currents or phase voltages of a three-phase polyphase machine, taking into account predetermined setpoint values. Manipulated variables Ud, Uq are then usually converted into trigger pulses for a pulse-width-modulation inverter, which adjusts the sinusoidal phase voltages (U, V, W) of the electric machine. An electric machine is usually regulated at low rotational speeds in PWM operation (PWM=pulse width modulation) and at high rotational speeds in block operation.
A regulating device in which the type of triggering may be switched between PWM and block operation as a function of rotational speed is also known from the related art.
FIG. 1 shows such a regulating device with which switching between PWM operation and block operation is possible. The regulating device includes essentially a software component 1 and a hardware component 2, software 1 generating various control signals dcU, dcV, dcW, epsilon, which are sent to hardware 2. Hardware 2 generates from these signals PWM signals TP_X_PWM (X here stands for phases U, V, W) and block signals TP_X_block, which are sent to pulse-width-modulation inverter 12 at low and high rotational speeds n, respectively.
Specifically, software 1 includes a device 6 for field-oriented regulation, determining a direct-axis voltage Ud and a quadrature-axis voltage Uq as manipulated variables of engine regulation (in a Cartesian coordinate system) from the actual value of the regulated variables, e.g., the phase voltages or currents of electric machine 14, taking into account a predetermined setpoint (e.g., for a setpoint torque or a setpoint output voltage). Manipulated variables Ud, Uq are sent to a software unit 4, also referred to as an inverse Park transformer that transforms direct-axis voltage Ud and quadrature-axis voltage Uq into PWM control signals dcX (signal 20), which are sent to hardware 2, taking into account angular displacement alpha.
Software 1 also includes a unit 5 for generating a block control signal, namely a delay angle epsilon in the present case. Direct-axis voltage Ud and quadrature-axis voltage Uq are also sent to unit 5. The equation for calculating the delay angle is:   epsilon  =      arctan    ⁢                   ⁢          Ud      Uq      
In addition, software 1 also includes a device 7 for calculating the rotational speed, calculating a rotational speed n from the change in angular displacement alpha over time, this rotational speed n being sent to a device 3 for selecting a triggering mode. Triggering mode selector device 3 controls a switch device 11 implemented as hardware which permits switching between PWM operation and block operation.
Hardware 2 includes a PWM unit 8 for generating PWM signals which are sent to switch device 11. At its input, PWM unit 8 receives PWM control signals dcX from inverse Park transformer 4 and generates PWM signals from them.
Hardware 2 also includes a block switch mechanism 9 for generating block signals TP_X_block, which are also sent to switch device 11. At its input, block switch mechanism 9 receives delay angle epsilon, which is calculated by unit 5 and is switched directly by angular displacement alpha.
Switch device 11, at whose input PWM signals and block signals are both applied for triggering pulse-width-modulation inverter 12, is triggered by selector device 3, so that at low rotational speeds below a predetermined rotational speed threshold, PWM signals TP_X_PWM are switched through to pulse-width-modulation inverter 12, and at higher rotational speeds above the rotational speed threshold, block signals TP_X_block are switched through to pulse-width-modulation inverter 12.
FIG. 2 shows a simplified version of a typical example of a pulse-width-modulation inverter, only a portion of pulse-width-modulation inverter 12 being shown for a phase U. Pulse-width-modulation inverter 12 includes two series-connected switches 30, 31, e.g., MOS transistors triggered by a signal TP_U. Because of the inversion of signal TP_U in the lower branch of the configuration, switches 30, 31 operate in opposition. When closed, switch 30 pulls phase signal Ph_U to a positive intermediate voltage +Uzw (switch 31 is open in this state). However, when switch 31 is closed (switch 30 is open in this state), switch 31 pulls phase potential Ph_U to a negative intermediate voltage −Uzw. Switches 30, 31 are triggered either by PWM signals TP_U_PWM in PWM operation or by block signals TP_U_block in block operation.
Regulating device 1, 2 also includes a position sensor 13 from whose output signals B0, B1, B2 a device 10 determines angular displacement alpha.
In the regulating device illustrated in FIG. 1, PWM signals TP_X_PWM and block signals TP_X_block are generated by two separate hardware units 8 and 9, respectively. However, generation of PWM signals and block signals by different devices is relatively complex, because a special control unit having two such hardware units must be made available.